1. Field of the Invention
The present invention relates to a catalyst for .alpha.-olefin polymerization and a process for producing an .alpha.-olefin polymer. More specifically, the present invention relates to a catalyst for .alpha.-olefin polymerization which provides an .alpha.-olefin polymer having a high isotacticity, containing an extremely small amount of a catalyst residue and an amorphous polymer and being excellent in mechanical properties and a processability, at an extremely high catalytic activity based on a solid catalyst component and on titanium atom, and a process for producing an .alpha.-olefin polymer
2. Description of the Related Arts
It has been well known as a process for producing isotactic polymers of an .alpha.-olefin (e.g., propylene, 1-Butene) that so-called Ziegler-Natta catalyst comprising a solid catalyst component obtained by using a transition metal compound of Groups 4 to 6 of the Periodic Table and specific organometallic compounds.
When an .alpha.-olefin polymer is produced, an amorphous polymer is produced in addition to a highly stereoregular .alpha.-olefin polymer having a high value for industrial application. The amorphous polymer has a little value for industrial application and badly influences mechanical properties when the .alpha.-olefin polymer is molded to a shaped article, a film, a fiber or other fabricated articles to be used. Further, the by-production of the amorphous polymer causes a loss of a raw material monomer, and at the same time, equipment for removing the amorphous polymer is required, which causes a disadvantage from an industrial view point. Therefore, it is preferable that a catalyst used for producing an .alpha.-olefin polymer has no formation of such an amorphous polymer, or scarcely little even if formed.
Further, catalyst residues of the transition metal component and the organometallic component remain in the .alpha.-olefin polymer obtained. Equipment for removing the catalyst residues is required for removal and deactivation of the catalyst residues, because the catalyst residues may cause problems in various points such as the stability and processability of the .alpha.-olefin polymer and the like.
The problem can be improved by increasing the catalytic activity which is represented by the weight of the produced .alpha.-olefin polymer per unit weight of the catalyst, and the above-mentioned equipment for removing catalyst residues becomes unnecessary, and it can reduce the production cost of the .alpha.-olefin polymer.
It is known that a Ti--Mg complex-type solid catalyst which is obtained by reducing a tetravalent titanium compound with an organomagnesium compound in the presence of an organosilicon compound to form an eutectic crystal of magnesium and titanium, can realize .alpha.-olefin polymerization of relatively high stereoregularity and high activity by being used in combination with an organoaluminum compound as a co-catalyst and an organosilicon compound as a third component to the polymerization (Japanese Patent Publication (Examined) Hei No.3-43283 and Japanese Patent Publication (Unexamined) Hei No.1-319508).
It is disclosed that a polymerization giving higher stereoregularity and higher activity can be realized by the coexistence of an additional ester when a tetravalent titanium compound is reduced with an organomagnesium compound in the coexistence of an organosilicon compound, in the above-mentioned process (Japanese Patent Publication (Unexamined) Hei No.7-216017).
Further, it is known that a highly stereoregular .alpha.-olefin polymer can be produced at a high polymerization activity with a solid catalyst synthesized by treating a reaction product of an organomagnesium compound with an alcohol, with titanium tetrachloride, an alkoxy titanium compound and phthaloyl chloride and then repeating contact treatment with titanium tetrachloride 3 times (Japanese Patent Publication (Unexamined) Hei No.8-231630).
A process free from an extraction and deashing is at the possible level, but further improvement is desired. Specifically, it is desired that highly stereoregular polymerization is realized without sacrificing a particle size distribution and the like in order to make an .alpha.-olefin polymer of high quality. In particular, since a highly stereoregular polymer directly causes a quality of high rigidity in a use for an injection molding field in which a polymer of high rigidity is desired, the appearance of a catalyst having a capability for a polymerization of higher stereoregularity, has been desired.
Further, when a solid catalyst such as the Ziegler-Natta catalyst is used for industrial application, its particle shape and particle size distribution are very important for controlling the bulk density of a polymer, particle size and flowability. With respect of improving the particle shape and narrowing the particle size distribution, trials to overcome these problems have been carried out, using a solid catalyst prepared by supporting a titanium-magnesium compound on a silica gel in the polymerization of ethylene (Japanese Patent Publication (Unexamined) Show No.54-148098 and Japanese Patent Publication (Unexamined) Show No.56-47407).
It is disclosed in Japanese Patent Publication (Unexamined) Sho No.62-256802 that particle properties are markedly improved by using a solid catalyst obtained by impregnating a titanium-magnesium compound in silica gel, in the polymerization of propylene.
Although an improvement effect on particle shape is surely recognized according to these processes, it is not preferable from a quality viewpoint that a large amount of silica gel used as the carrier remains in the final products, which happens to cause fish eye in film use. Further, polymerization activity is also low and productivity cannot be satisfied. Accordingly, a solid catalyst component having an excellent catalyst shape and narrow particle size distribution and a polymerization capability of high activity and high stereoregularity is seriously desired.